Program instrumentation method and apparatus for constraining the behavior of embedded script in documents

Abstract

A method and apparatus is disclosed herein for constraining the behavior of embedded script in documents using program instrumentation. In one embodiment, the method comprises downloading a document with a script program embedded therein, inspecting the script program, and rewriting the script program to cause behavior resulting from execution of the script to conform to one or more policies defining safety and security. The script program comprises self-modifying code (e.g., dynamically generated script).

Description

PRIORITY [0001] The present patent application claims priority to and incorporates by reference the corresponding provisional patent application Ser. No. 60 / 816,679, entitled, “Program Instrumentation Method and Apparatus for Constraining the Behavior of Embedded Script in HTML Documents”, filed on Jun. 26, 2006.FIELD OF THE INVENTION [0002] The present invention relates to the field of computer programming; more particularly, the present invention relates to controlling (e.g., constraining) the behavior of embedded script in documents (e.g., HTML documents). BACKGROUND OF THE INVENTION [0003] JavaScript has become a popular tool in building web pages. JavaScript programs are essentially a form of mobile code embedded in HTML documents and executed on client machines. With help of the Document Object Model (DOM) and other browser features, JavaScript programs can obtain restricted access to the client system and improve the functionality and appearance of web pages. [0004] As is the...

AI Technical Summary

Problems solved by technology

As is the case of other forms of mobile code, JavaScript programs introduce potential security vulnerabilities and loopholes for malicious parties to exploit.

Unfortunately, this feature has been heavily exploited to generate annoying pop-ups of undesirable contents, some of which are difficult to “control” from a web user's point of view (e.g., control buttons out of screen boundary, instant respawning when closed).

More severely, this feature has also been exploited for launching phishing attacks, where key information about the origin of the web page is hidden from users (e.g., a hidden location bar), and false information assembled to trick users into believing malicious contents (e.g., a fake location bar).

For instance, JavaScript code from attacker.com will not be able to read a cookie set by mybank.com.

Unfortunately, many web applications exhibit XSS vulnerabilities, where a malicious piece of script can be injected into a web page produced by a vulnerable application.

The situation is potentially worse than for other forms of mobile code such as application downloading, because the user may not realize that loading web pages entails the execution of untrusted code.

These only provide limited (coarse-grained) protections.

There remain many opportunities for attacks, even if these protections are perfectly implemented.

In practice, it is sometimes difficult to deploy multiple solutions all together.

In addition, there are many attacks that are outside of the range of protection of existing tools.

None of these prior protection methods rewrite the code.

They help well-intended programmers to build web applications that are free of certain vulnerabilities, but cannot prevent malicious code from harming the client through browser-based attacks.

However, these previous techniques address specific questions including memory safety, debugging and testing, and data collection.

They do not address browser safety and security questions.

In addition, they are not sufficient for regulating the behavior of embedded JavaScript in HTML documents.

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